I would strongly advise AGAINST frontloading your TSP and then stopping contributions later in the year. Yes, this gives you more "time in market" for your dollars, but you will miss out on the matching funds.

The federal employer matching funds for the TSP are 5% per paycheck, not 5% of your total annual contribution. They will put in 5% of your paycheck each pay period, if you also put in at least 5% per pay period. So if you're making 70k you are entitled to an extra $3500 in TSP match (that's 5% of 70k) but only if you contribute each and every pay period. If you were to do 100% TSP allocation of your 70k paycheck, you'd be putting in about $2700 every two weeks and would max out the 19k limit in only seven pay periods, then you wouldn't be allowed to put in any more. You'd get 5% of your first 7 paychecks matched, about $135 for each check times 7 would be $945 in matching added to your TSP, instead of the $3500 you could get by spreading out your contributions over all 26 pay periods.

You'd end up costing yourself 3500-945 is $2555, in lost TSP contributions. Don't be that guy. The approach normally recommended for folks who want to max it out is to put in $731 from each of their 26 paychecks, to hit the 19k limit at the end of the year and maximize the matching funds regardless of salary level.

In your case, it probably makes sense to figure out how much you've already contributed for 2019 and how many pay periods you have left, then do the math to spread out the remainder of your 19k limit over the whole year. If you're making 70k, you only need to contribute $135 per paycheck to get your full match each pay period. It adds up. Try not to leave money on the table.